Multilayer plastic containers and preforms typically include one or more layers of plastic matrix resin such as polyethylene terephthalate (PET) alternating with one or more layers of barrier resin such as polyamide or ethylene vinyl alcohol (EVOH) to resist transmission of gas, water vapor and/or flavorants, including odorants and essential oils, through the container wall. An important property of containers of this type is interlaminar adhesion to resist delamination between or among the various layers during filling and handling of the containers by the container manufacturer and the product packager, and during use of the container by the consumer, and there is a need for increasing interlaminar adhesion without detrimentally affecting other container features, such as barrier properties and container clarity. It is therefore a general object of the present invention to provide a multilayer container, a container preform, a multilayer article of manufacture, a method of manufacture and a barrier resin blend having improved adhesion characteristics between the layers of the preform and the container made therefrom.
A plastic container in accordance with one presently preferred aspect of the invention includes a multilayer wall having at least one layer of matrix resin, at least one layer of barrier resin, and an adhesion-promoting material blended with the barrier resin and/or the matrix resin to promote bonding between the barrier and matrix layers. In the preferred embodiments of the invention, the adhesion-promoting material is blended with the barrier resin. The adhesion-promoting material is an amine polymer, preferably an imine polymer, having a plurality of available primary, secondary, or tertiary amine groups. Such polyamine polymers preferably are an alkylene imine polymer or an alkylene amine polymer. Alkylene imine polymers, particularly polyethyleneimine (PEI) polymers, are particularly preferred. PEI polymers are sold by Nippon Shokubai Co., Ltd. under the trade name Epomin, and the EPOMIN bulletin published by Nippon Shokubai Co., Ltd. is incorporated herein by reference.
The polyamines of the present invention are polymeric, either homopolymeric or copolymeric polyamines, and preferably is an alkylene amine polymer or an alkylene imine polymer having molecular weights of from about 150 to about 2,000,000, with about 150 to about 400,000 preferred, and most preferred being from about 300 to about 80,000. Examples of polyamines useful for the invention include polyvinyl amines, aminofunctional polyacrylamides, polyDADMAC's, polyvinyl pyrrolidone copolymers, polyethyleneimine, polypropyleneimine and the reaction product of ethylene diamine and epichlorohydrin copolymers.
A preferred polyamine that can be used to achieve adhesion promoting characteristics is the class of polyamines referred to as polyalkylenimines, such as polyethyleneimine, which is readily available in a wide range of molecular weights and different degrees of branchings. Polyethyleneimines consist of a large family of water-soluble polyamines of varying molecular weight and degree of chemical modification. It is generally known that the polymerization of ethylenimine does not result in a polymer that is completely composed of units having a linear structure, but that also the degree of branching in polyethyleneimines depends on the acid concentration and the temperature during polymerization. Additional groups may be grafted onto polyethyleneimines using methods well known in the art to change other desirable physical and chemical properties. Preferred molecular weights of the polyethyleneimine are from about 150 to 80,000. Most preferred molecular weights of the polyethyleneimine are from about 300 to 80,000 for reasons of material viscosity. As an additional feature of the present invention, PEI polymers blended in the barrier or matrix layer can also interact with acidic gases such as carbon dioxide to provide enhanced acidic gas barrier polymers, to provide increased carbon dioxide barrier performance of the container. This is particularly useful in reducing carbon dioxide loss from the package when the resulting container is used to package carbonated beverages such as soft drinks or beer.
The matrix polymer preferably is an ester-containing polymer—i.e., polymers having an ester in the main polymer chain, ester moities grafted to the main polymer chain, or ester moities as side groups to the chain. Polyester resin is particularly preferred. The polyester resin may be any suitable polyester resin having an ester in the main polymer chain. Suitable polyesters include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate (PPT), polyethylene naphthalate (PEN), polyglycolic acid (PGA), polycarbonate (PC) and polylactic acid (PLA). Other suitable matrix polymers include polyacrylates such as polymethyl methacrylate (PMMA), polyethylene methacrylate (PEMA) and vinyl acetates. Also usable are blends and copolymers of the above, and process and post-consumer regrind that consists essentially of the above, or blends or copolymers of the above. PET-based resins, blends, copolymers and regrinds are particularly preferred. Other matrix polymers include polyolefins and polyamides.
The PEI polymers are known to carry a high cationic charge density by virtue of their incorporation of high amounts of primary, secondary and tertiary amine functionalities. While not being bound to any particular theory, it appears that these amine functionalities strongly interact with esters or other functional groups to achieve improved adhesion between the barrier and ester-containing layers to reduce or prevent delamination of the wall layers during handling and use of the containers.
The barrier resin preferably is selected from the group consisting of EVOH, polyamide, acrylonitrile copolymers, blends of EVOH and polyamide, nanocomposites of EVOH or polyamide and clay, blends of EVOH and an ionomer, acrylonitrile, cyclic olefin copolymers, polyvinylidene chloride (PVDC), polyglycolic acid (PGA), and blends thereof. EVOH and meta-xylylenediamine (MXD) polyamide are particularly preferred. The invention thus achieves improved adhesion between the barrier and polyester layers to reduce or prevent delamination of the wall layers during handling and use of the containers.
Other aspects of the invention include a plastic container preform, methods of making a plastic container and a preform, a barrier resin blend, and a multilayer article and method of manufacture in accordance with the invention.